It has become common to treat many diseases using implantable medical devices (IMDs) that are chronically implanted within the body of a patient. Examples of such medical devices include pacemakers, defibrillators, drug-delivery devices, and electro-stimulators for stimulating nerves, muscles, and other tissue.
In spite of all precautions, bacterial colonization of implanted medical devices remains a serious complication. For pacemaker leads, for example, it is believed that about 10% of leads will fail or become infected, requiring removal. In approximately 27% of the operations to remove pacemaker leads, infection is reason for removal. Chronic pacemaker lead-centered infections can occur and can lead to serious complications including death. The literature overwhelmingly indicates that where possible, infected hardware must be removed in order to insure that the infection is cured.
Prevention of the infection in the first place would be a preferred alternative. The use of antimicrobial coatings on pacemaker leads not been successful for several reasons. One is that some patients can develop serious reactions to certain antimicrobial chemicals. Another is that lead centered infections typically occur chronically, primarily after reintervention. That is, when an implantable medical device (IMD) in general, or pacemaker lead in particular, is implanted, the infection rate is very low. However, the infection rate rises significantly when the IMD is subsequently adjusted or renewed. For example, when a pacemaker is first implanted, the infection rate for the leads approaches zero. If there is reintervention to replace the pacemaker pulse generator, which is located within a fibrous tissue capsule, then infection at the leads and around the capsule is more likely. Given that most antimicrobial coatings involve elution of the drug, the coating becomes ineffective long before it is needed.
The use of silver ion has been promoted as bactericidal. Silver received a bad name because it apparently also inhibits the healing process, resulting in blood leakage around treated valve sewing rings, for example. No effective long-term means of preventing or reducing device centered infection has yet been described.